API edits to avoid implying that JSON-LD is not RDF

As promised, attached are suggested edits to the "JSON-LD 1.0 Processing
Algorithms and API" document at

  http://json-ld.org/spec/latest/json-ld-api/index.html

The purpose of these edits is to avoid implying that JSON-LD is not RDF.

The main strategy was to change phrases like "transforms JSON-LD to
RDF" and "converts RDF to JSON-LD" to phrases like "deserializes JSON-LD
to RDF" and "serializes RDF to JSON-LD".

Note that some of the section titles changed as a result, and two HTML
anchors were also changed:

  convert-to-rdf-algorithm --> deserialize-to-rdf-algorithm

  convert-from-rdf-algorithm --> serialize-from-rdf-algorithm

Therefore other documents that reference this document may need to
be updated correspondingly.
Fix markup

No other changes
Minor tweaks to make it clearer what the algorithms are supposed to do
Merge pull request #287 from lanthaler/dbooth-api-spec-changes

David Booth's API edits to avoid implying that JSON-LD is not RDF